Background: Despite numerous publications about the management of the anemia of chronic kidney disease (CKD) its best management remains controversial, and the need for continued improvement is a stated priority in the National Kidney Foundation-Kidney Disease Outcomes Quality Initiative (NKFKDOQI) Clinical Practice Guidelines for patients with CKD. Specific aim 1: In hemodialysis patients, determine the relation between hemoglobin concentration and dosing patterns of erythropoietin and parenteral iron. Hypothesis: The erythropoietin and iron doses most closely associated with target hemoglobin are consistent with the NKF-KDOQI guidelines recommended doses. Specific aim 2: In hemodialysis patients, determine the relation between hemoglobin concentration and survival.Hypothesis: Most favorable survival is associated with mean hemoglobins that include the NKF-KDOQI guidelines' target range. We will address these aims using prospectively collected individual-level patient data from up to 10,000 hemodialysis patients in the American arm of the Dialysis Outcomes and Practice Patterns Study (DOPPS). Enrollment for the DOPPS began in 1996 and is ongoing. For both specific aims, we will investigate causality by controlling for time-varying and bidirectional associations.